A sensor using surface plasmon resonance has been known as highly sensitive measuring means of a trace analyte and optical property of an analyte until now.
A typical surface plasmon resonance sensor makes a metal thin film, provided in an end face of an ATR prism coupler, generate surface plasmon in resonance to measure the optical properties of the analyte disposed in the vicinity of it with high sensitivity. Since it is possible to read unique information of an analyte in optical properties such as a refractive index, absorption, and a fluorescent characteristic, it is also possible to apply a surface plasmon resonance sensor also as a biosensor.
It is described in Jiri Homola, et al., Sensors and Actuators B, Vol. 54, 3 (1999) that sensitivity of a surface plasmon resonance sensor is excellent in a visible region. For example, in angular interrogation of a typical sensor device using an ATR prism coupler (BK7 glass as an ATR prism coupler medium, 50 nm gold as a metal thin film, and 1.32 of refractive index of an analyte), sensitivity S(pθ) defined by a refractive index change and a resonance condition change of the analyte shows a value of 100 to 200 [deg/RIU]. Assuming an angular resolution of a typical system (1×10−4 [deg]), this value means that it is possible to measure even such an extremely minute change that a refractive index change of the analyte is 5×10−7 to 1×10−6 [RIU]. On the other hand, recently, it has being known that features of optical properties of sugar, protein, and the like exist also in a frequency region from a millimeter wave band to a terahertz band, and importance of applying a surface plasmon resonance sensor in a visible region to a frequency region from a millimeter wave band to a terahertz band is high. However, according to Jiri Homola, et al., Sensors and Actuators B, Vol. 54, 16 (1999), it is described that the sensitivity S(pθ) drops with a longer wavelength of an electromagnetic wave to be used.
In addition, although Japanese Patent Application Laid-Open No. 2004-354246 discloses a sensor device using a prism in a terahertz band, it does not become highly sensitive measuring means of optical properties of an analyte since an electric field enhancing effect generated at the time of surface plasmon resonance is not obtained because of nonresonant structure.
Hence, also in the frequency region from 30 GHz to 30 THz, or from a millimeter wave band to a terahertz band, a sensor which has the sensitivity to the extent currently used in a visible region has been requested.
The present invention aims at providing a surface plasmon resonance sensor in the frequency region from a millimeter wave band to a terahertz band, from 30 GHz to 30 THz which solves the above-mentioned tasks and has sensitivity comparable to a surface plasmon resonance sensor in a visible region.